The distribution and content of hydrocarbon-containing fluid changes over time in a reservoir and many, more or less successful, attempts have been made to predict this development. The use of sensors measuring different fluid properties is one way of obtaining data for such prediction. The sensors are inserted into the formation along the borehole, and during measurements the sensors obtain vibrations from a seismic source located at the seabed or at surface. The vibrations change as the vibrations develop in the formation, and from the received vibrations in the sensors, the distribution and content of hydrocarbon-containing fluid in the reservoir can be analysed. Based on these predictions, the inflow valves, and thus the production zones, are adjusted so that the reservoir is emptied from hydrocarbons in a more optimal manner.
It is a problem that sensors drift over time due to the high temperatures and pressures, and the reliability of these sensor measurements is hence diminished to such an extent that accurate prediction is impossible.